1. Field of the Invention
This invention relates to clocks and more particularly to a setting mechanism for estimated time of arrival clock hands.
2. Prior Art
It has been known to provide an extra set of minute and hour hands on a clock which may be manually set for an estimated time of arrival (ETA) at a particular destination. Such a mechanism is particularly useful in an automobile or aircraft clock in which the hands can be set to a predetermined time up to 12 hours in the future on a 12-hour clock, or up to 24 hours on a 24 hour clock. The actual time indicated can be readily compared to the ETA at a particular destination. Previous clocks having ETA hands have utilized means for setting ETA hour and minute hands which is awkward, inconvenient, and difficult to manufacture since large numbers of parts are involved. Since ETA clocks are most useful in moving vehicles, it is important that the operator be able to quickly set the ETA hour and minute hands without being distracted from operation of the vehicle, and that once set, the ETA setting is vibration resistant.
United States Letters Patent No. 1,790,359 to Weir illustrates one example of a prior art ETA clock having the above described disadvantages. Weir discloses an ETA minute hand and ETA hour hand provided in addition to the normal minute and hour hands for indicating present time. A single knob is positioned on the front of the clock crystal which directly drives or controls the ETA minute hand. The ETA hour hand, however, is coupled to the minute hand by a reduction gear. Therefore, the knob in Weir must be rotated one complete revolution for each hour change. Therefore, in the case of 12-hour clock, up to six revolutions may be required to set the minute and hour hands, assuming bi-directional knob rotation.
In United States Letters Patent No. 3,837,161 to Wuthrich, a regular and an auxiliary hour hand rotate together in one direction and rotate relative to one another in the opposite direction. Such an arrangement is inappropriate for an ETA clock setting since, once set, the ETA hands remain stationary.
United States Letters Patent No. 2,645,077 to Olson describes the use of two knobs aligned in coaxial fashion which can be locked together in common rotation by insertion of a tool. Use of such a tool would be inconvenient for one wishing to set ETA time rapidly.
The Wakmann Watch Company has marketed clocks providing ETA hour and minute hands. However, in the Wakmann devices known to me, a single knob is employed and sets the ETA hour hand via a gear reduction, as in Weir, or via a one-way clutch which sets the ETA hour hand by counterclockwise rotation and the ETA minute hand by clockwise rotation whereby an accidential overshoot in setting either hand makes proper reverse setting annoying to the operator.